cant play dvds

I own an acer aspire 5920 laptop running windows 7. the problem i have is that dvds arent recognised in the drive and wont play. CD's are fine and the settings in control panel are for dvds to play automatically in media player. this only happened recently and i dont know how to solve it can anyone help.

Problems in Device Manager - try uninstalling and reinstalling the DVD player or if it gives an error code there then

No CD/DVD or CD-ROM access is missing error Code 19, Code 31, Code 32, Code 39, or Code 41
Try this if the optical drives are not appearing in My Computer or Device Manager.
(This is sometimes caused by the removal of Roxio or other writing software.)

http://www.dougknox.com/xp/utils/XP_CD-DVD-Fix.zip
Download XP_CD-DVD-Fix.zip and save this file to your hard drive. Navigate to where you saved it and double click the file to extract the contents. Locate the EXE file you extracted and double click it. A confirmation dialog will appear when the script is done. You may need to reboot for the change to take effect.
This utility is only intended for Windows® XP, but also appears to work for Vista and Windows 7.
You may need Administrator level access to use this utility. If you do not have Administrator level access, the program will say it is finished, but will not have made any changes.

Similar fixes
http://support.microsoft.com/kb/314060/ works for vista or XP
http://aumha.org/downloads/cdgone.zip

or manual fix
Run regedit and navigate to registry key
HKEYLOCALMACHINE\SYSTEM\CurrentControlSet\Control\Class\ {4D36E965-E325-11CE-BFC1-08002BE10318}.
Highlight it and in the right pane, find the Upperfilters and Lowerfilters values.
Highlight each one in turn, right click and delete them.
Close regedit and restart the computer.
If in doubt make a restore point before making changes.